Fix out of date column header when creating from POT.
Yet more fixes for crashes due to changing screens.
Exception::what() should be const.
Add Catalog::SetFileName() helper.
Fix case of the File->New XXX entries on Windows.

Accidentally used titlecase, that's not what should be done on Windows.
Make the welcome screen buttons a bit wider on OS X.
Pass --from-code=UTF-8 to xgettext.

Now that Poedit sources use Unicode characters, it became necessary.
Update poedit.pot and *.po files.

This wasn't done since 1.4, so it's about time, in preparation for the
1.6 release...
Don't show the merge summary by default.